All in all, it works fairly well, BUT...there are some phrases and letters that seem to be very difficult sounds and letters for the microphones to pick up correctly. V's, B's, D's, T's and R's often have problems (compounded by the fact that they are pronounced differently from one Spanish-speaking country to another), and I also seem to have troubles with exclamations (like "Ah..." and "Ay..."), and also sentences that begin with "Él".
There are a few others, and I'm really not sure if there is any way to address the issue. I don't care to set my Rocket Record Difficulty lower than "Hard", because I am very familiar with the timbre and the timing of Spanish, and I can usually score 100%, but with the examples above, I can sometimes only score 75%. I can usually let it go as a quirk to the technology of voice recognition, but I would be lying if I didn't admit that it can be very frustrating, particularly when you KNOW you are saying something correctly.
I'm curious where the rest of you have your Rocket Record Difficulty set at, and what type of microphone you use, and if you experience any of the same issues that I do with the voice recognition.